Identification of the pcaRKF gene cluster from Pseudomonas putida: involvement in chemotaxis, biodegradation, and transport of 4-hydroxybenzoate

J Bacteriol. 1994 Nov;176(21):6479-88. doi: 10.1128/jb.176.21.6479-6488.1994.


Pseudomonas putida PRS2000 is chemotactic to 4-hydroxybenzoate and other aromatic acids. This behavioral response is induced when cells are grown on 4-hydroxybenzoate or benzoate, compounds that are degraded via the beta-ketoadipate pathway. Isolation of a transposon mutant defective in 4-hydroxybenzoate chemotaxis allowed identification of a new gene cluster designated pcaRKF. DNA sequencing, mutational analysis, and complementation studies revealed that pcaR encodes a regulatory protein required for induction of at least four of the enzymes of the beta-ketoadipate pathway and that pcaF encodes beta-ketoadipyl-coenzyme A thiolase, the last enzyme in the pathway. The third gene, pcaK, encodes a transporter for 4-hydroxybenzoate, and this protein is also required for chemotaxis to aromatic acids. The predicted PcaK protein is 47 kDa in size, with a deduced amino acid sequence indicative of membership in the major facilitator superfamily of transport proteins. The protein, expressed in Escherichia coli, catalyzed 4-hydroxybenzoate transport. In addition, whole cells of P. putida pcaK mutants accumulated 4-hydroxybenzoate at reduced rates compared with that in wild-type cells. The pcaK mutation did not impair growth at the expense of 4-hydroxybenzoate under most conditions; however, mutant cells grew somewhat more slowly than the wild type on 4-hydroxybenzoate at a high pH. The finding that 4-hydroxybenzoate chemotaxis can be disrupted without an accompanying effect on metabolism indicates that this chemotactic response is receptor mediated. It remains to be determined, however, whether PcaK itself is a chemoreceptor for 4-hydroxybenzoate or whether it plays an indirect role in chemotaxis. These findings indicate that aromatic acid detection and transport are integral features of aromatic degradation pathways.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Acetyl-CoA C-Acyltransferase / genetics
  • Amino Acid Sequence
  • Bacterial Proteins / genetics
  • Base Sequence
  • Benzoates / metabolism
  • Benzoic Acid
  • Biodegradation, Environmental
  • Biological Transport
  • Carrier Proteins / genetics
  • Chemotaxis
  • Cloning, Molecular
  • Escherichia coli / genetics
  • Genes, Bacterial / genetics*
  • Membrane Transport Proteins*
  • Molecular Sequence Data
  • Multigene Family / genetics*
  • Mutation
  • Parabens / metabolism*
  • Pseudomonas putida / genetics*
  • Recombinant Proteins / metabolism
  • Sequence Analysis, DNA
  • Succinates / metabolism
  • Succinic Acid


  • Bacterial Proteins
  • Benzoates
  • Carrier Proteins
  • Membrane Transport Proteins
  • Parabens
  • PcaK protein, Pseudomonas
  • Recombinant Proteins
  • Succinates
  • Benzoic Acid
  • Succinic Acid
  • Acetyl-CoA C-Acyltransferase
  • 3-oxoadipyl-coenzyme A thiolase
  • 4-hydroxybenzoic acid

Associated data

  • GENBANK/L33795
  • GENBANK/U10895